Browser extensions allow developers to add functionality to the browser and enhance the user interface in a way that is not directly related to the viewable content of webpages. This class of extensibility includes add-on functionality that users might install to enhance their browsing experience. A toolbar is one example of a browser extension. A browser toolbar is a toolbar that resides within a browser's window and is a way to extend the browser's user interface and functionality. Browser extensions can have access to everything done by the browser, and can do things like inject ads or other content into webpages, or make “background” Hypertext Transfer Protocol (HTTP) requests to a third-party server. This power can be abused by browser extensions; while webpages are constrained by the security model of the web, extensions are not. As a result, a browser extension may not behave as described, and take action against the interest of the user who installed it. Such browser extensions are a form of malware.